Preprints
Filtering by Subject: Geophysics and Seismology
The detection of low magnitude seismic events using array-based waveform correlation
Published: 2017-11-08
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
It has long been accepted that occurrences of a known signal are most effectively detected by cross-correlating the incoming data stream with a waveform template. Such matched signal detectors have received very little attention in the field of detection seismology because there are relatively few instances in which the form of an anticipated seismic signal is known a priori. Repeating events in [...]
The European Arctic: A Laboratory for Seismoacoustic Studies
Published: 2017-11-08
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
We describe the seismoacoustic monitoring network in Fennoscandia and North West Russia and present how it is being used to characterize infrasound studies in that part of the world. The history of the infrasound array network is presented, together with a description of array processing considerations, and examples of infrasound signals recorded from repeating explosions.
Collinearity assessment of geocentre coordinates derived from multi-satellite SLR data
Published: 2017-11-08
Subjects: Earth Sciences, Geophysics and Seismology, Other Earth Sciences, Physical Sciences and Mathematics
Of the three satellite geodetic techniques contributing to the International Terrestrial Reference Frame (ITRF), Satellite Laser Ranging (SLR) is generally held to provide the most reliable time series of geocentre coordinates and exclusively defines the ITRF origin. Traditionally, only observations to the two LAser GEOdynamics Satellite (LAGEOS) and Etalon pairs of satellites have been used for [...]
Seismotectonics of a diffuse plate boundary: Observations off the Sumatra-Andaman trench
Published: 2017-11-05
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
Seismic slip extends from maximum expected depth through the crust in 45-75 Ma oceanic lithosphere in the Indo-Australian intraplate region off the Sumatra-Andaman trench. Large (magnitude greater than 7) strike-slip earthquakes in this region can rupture multiple differently oriented faults. Rupture directivity modeling provides tentative support for active east-west oriented faults.
Data quality of collocated portable broadband seismometers using direct burial and vault emplacement
Published: 2017-11-05
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
Temporary broadband sensor deployments have traditionally been predominantly emplaced using shallow vaults that require more materials, personnel, and time than direct burial. However, new developments in seismometer and seismograph technology are increasingly facilitating systems that can be directly buried in earth or snow without vault enclosures. We analyze data from two identical shallow [...]
Could the IMS Infrasound Stations Support a Global Network of Small Aperture Seismic Arrays?
Published: 2017-11-05
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
The IMS infrasound arrays have up to 15 sites with apertures up to 3 km. They are distributed remarkably uniformly over the globe, providing excellent coverage of South America, Africa, and Antarctica. Therefore, many infrasound arrays are in regions thousands of kilometers from the closest seismic array. Existing 3-component seismic stations, co-located with infrasound arrays, show how typical [...]
The 2015 MW 7.1 Earthquake on the Charlie-Gibbs Transform Fault: Repeating Earthquakes and Multi-modal Slip on a Slow Oceanic Transform
Published: 2017-11-04
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
The slow spreading rate Charlie-Gibbs Atlantic transform fault slips in large (M~7) quasi-repeating earthquakes. The foreshocks, aftershocks, and unilateral rupture of the 2015 earthquake are similar to a 1974 earthquake on the same transform. The findings of this study are consistent with transform earthquakes starting small near the ridge and large slip asperities nearer to the transform center.
Iterative Strategies for Aftershock Classification in Automatic Seismic Processing Pipelines
Published: 2017-11-04
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
Aftershock sequences following very large earthquakes present enormous challenges to near‐real‐time generation of seismic bulletins. The increase in analyst resources needed to relocate an inflated number of events is compounded by failures of phase‐association algorithms and a significant deterioration in the quality of underlying, fully automatic event bulletins. Current processing pipelines [...]
How do we understand and visualize uncertainty?
Published: 2017-11-03
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
Geophysicists are often concerned with reconstructing subsurface properties using observations collected at or near the surface. For example, in seismic migration, we attempt to reconstruct subsurface geometry from surface seismic recordings, and in potential field inversion, observations are used to map electrical conductivity or density variations in geologic layers. The procedure of inferring [...]
Three-dimensional variations in Love and Rayleigh wave azimuthal anisotropy for the upper 800 km of the mantle
Published: 2017-11-03
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
We present a new mantle model (YB14SHani) of azimuthal anisotropy for horizontally polarized shear waves (SH) in parallel with our previously published vertically polarized shear wave (SV) anisotropy model (YB13SVani). YB14SHani was obtained from higher mode Love wave phase velocity maps with sensitivity to anisotropy down to ~1200 km depth. SH anisotropy is present down to the mantle transition [...]
Structure and anisotropy of the Mexico subduction zone based on Rayleigh-wave analysis and implications for the geometry of the Trans-Mexican Volcanic Belt
Published: 2017-11-03
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
We develop a three-dimensional model of shear wave velocity and anisotropy for the Mexico subduction zone using Rayleigh wave phase velocity dispersion measurements. This region is characterized by both steep and flat subduction and a volcanic arc that appears to be oblique to the trench. We give a new interpretation of the volcanic arc obliqueness and the location of the Tzitzio gap in volcanism [...]
Radial anisotropy and prior petrological constraints: A comparative study
Published: 2017-11-03
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
Radial seismic anisotropy models are traditionally obtained using empirical constraints based on laboratory experiments and petrological considerations. We tested the hypothesis that such petrological constraints affect the uppermost mantle models of S wave anisotropy using a statistical approach. In addition, we were able to determine which model features are constrained by the data and which [...]
Radial anisotropy in seismic reference models of the mantle
Published: 2017-11-03
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
Sambridges Neighborhood Algorithm was applied to normal mode and surface wave phase velocity data to determine the likelihood of radial anisotropy in mantle reference models. This full model space search technique provides probability density functions for each model parameter and therefore reliable estimates of resolution and uncertainty, without having to introduce unnecessary regularization on [...]
Changes in Seismic Anisotropy Shed Light on the Nature of the Gutenberg Discontinuity
Published: 2017-11-03
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
The boundary between the lithosphere and asthenosphere is associated with a plate-wide high seismic velocity “lid” overlying lowered velocities, consistent with thermal models. Seismic body waves also intermittently detect a sharp velocity reduction at similar depths, the Gutenberg (G) discontinuity, which cannot be explained by temperature alone. We compared an anisotropic tomography model with [...]
Robust Normal Mode Constraints on Inner-Core Anisotropy from Model Space Search
Published: 2017-11-03
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
A technique for searching full model space that was applied to measurements of anomalously split normal modes showed a robust pattern of P-wave and S-wave anisotropy in the inner core. The parameter describing P-wave anisotropy changes sign around a radius of 400 kilometers, whereas S-wave anisotropy is small in the upper two-thirds of the inner core and becomes negative at greater depths. Our [...]